Power management is desirable for desktop personal computers and workstations because a typical desktop computer system can consume several hundred watts of power per hour when it is turned on, whether or not it is being used. This energy consumption can be quite expensive, particularly in the context of large companies and other institutions that may have hundreds or even thousands of desktop computer systems turned on both day and night. One way to reduce power consumption is to power manage the computer system by, for example, turning off peripheral devices that are not in use or slow down the processes that are running on the computer.
Energy Star (EStar) guidelines are power management guidelines issued by the U.S. Government's Environmental Protection Agency (EPA). EStar guidelines exist for many products, including desktop computers. EStar power management guidelines require specified reduction in power within a specified time for a computer system when no keyboard or mouse activity has been detected. For example, the proposed Memorandum of Understanding 3 (MOU-3) guidelines require the display framebuffer to be powered off after 30 minutes when no keyboard or mouse activities have been detected.
Powering down the framebuffer during power management may present problems to systems that are running window applications that do not require keyboard or mouse activities. For example, a clock tool may continuously update the time display in a window thus requiring access to the display framebuffer regardless of whether there are user activities at the keyboard or the mouse. If the computer system where the window is displayed enters power management mode while the clock tool is running, the clock tool continues to access the framebuffer even though the framebuffer is powered off. Access to the framebuffer when it is powered off causes the system to hang.